1. Field of the Invention
The present invention relates to a resist composition used in a manufacturing process of semiconductors, such as IC, manufacture of circuit substrates for liquid crystals, thermal heads and the like, and lithographic process of other photo-fabrication, and also relates to resins used in the resist composition, compounds for use in the synthesis of the resins, and a pattern-forming method using the positive resist composition. Specifically, the invention relates to a resist composition suitable for exposure with an immersion projection exposure apparatus using far ultraviolet rays of wavelengths of 300 nm or less as the light source, resins used in the resist composition, compounds for use in the synthesis of the resins, and a pattern-forming method using the positive resist composition.
2. Description of the Related Art
With the progress of fining of semiconductor elements, shortening of the wavelengths of exposure light source and increasing in the numerical aperture (high NA) of the projection lens have advanced, and now exposure apparatus of NA 0.84 using an ArF excimer laser having wavelength of 193 nm as the light source have been developed. As generally well known, these can be expressed by the following expressions:(Resolution)=k1·(λ/NA)(Depth of focus)=±k2·λ/NA2 wherein λ is the wavelength of the exposure light source, NA is the numerical aperture of the projection lens, k1 and k2 are the coefficients concerning the process.
For the realization of further higher resolution by the shortening of wavelengths, an exposure apparatus with an F2 excimer laser having wavelength of 157 nm as the light source has been studied, however, the materials of lens for use in the exposure apparatus and the materials for use in the resist for shortening of wavelengths are extremely restricted, so that the realization of the reasonable manufacturing costs of the apparatus and materials and quality stabilization are very difficult, as a result, there are possibilities of missing an exposure apparatus and a resist having sufficient performances and stabilities within a required period of time.
As a technique for increasing resolution in optical microscope, what is called immersion method of filling between a projection lens and a sample with a liquid of high refractive index (hereinafter also referred to as “immersion liquid”) has been conventionally known.
In connection with “the effect of immersion”, the above resolution and depth of focus can be expressed by the following expressions in the case of immersion, taking λ0 as the wavelength of the exposure light in the air, n as the refractive index of immersion liquid to the air, and NA0=sin θ with θ as convergence half angle of the ray of light:(Resolution)=k1·(λ0/n)/NA0 (Depth of focus)=±k2·(λ0/n)/NA02 
That is, the effect of immersion is equivalent to the case of using exposure wavelength of wavelength of 1/n. In other words, in the case of the projection optical system of the same NA, the depth of focus can be made n magnifications by immersion. This is effective for every pattern form, and it is possible to be combined with super resolution techniques such as a phase shift method and a deformation lighting method.
The apparatus applying this effect to the transfer of micro-fine image pattern of semiconductor element are introduced by JP-A-57-153433 and JP-A-7-220990.
The latest advancement of immersion exposure techniques is reported in SPIE Proc., 4688, 11 (2002), J. Vac. Sci. Tecnol. B, 17 (1999), and JP-A-10-303114. When an ArF excimer laser is used as the light source, it is thought that pure water (refractive index at 193 nm: 1.44) is most promising in the light of the safety in handling, and transmittance and refractive index at 193 nm.
When an F2 excimer laser is used as the light source, a solution containing fluorine is discussed from the balance of transmittance and refractive index at 157 nm, but a sufficiently satisfactory solution from the viewpoint of environmental safety and in the point of refractive index has not been found yet. From the extent of the effect of immersion and the degree of completion of resist, it is thought that immersion exposure technique will be carried on an ArF exposure apparatus earliest.
On and after the resist for a KrF excimer laser (248 nm), an image-forming method that is called chemical amplification is used as the image-forming method of the resist for compensating for the reduction of sensitivity by light absorption. To explain the image-forming method of positive chemical amplification by example, this is an image-forming method of exposing a resist to decompose an acid generator in the exposed part to thereby generate an acid, changing an alkali-insoluble group to an alkali-soluble group by the bake after exposure (PEB: Post Exposure Bake) by utilizing the generated acid as the reactive catalyst, and removing the exposed part by alkali development.
The resist for an ArF excimer laser (wavelength: 193 nm) using the chemical amplification mechanism is now being a main current, but many insufficient points still remain, and the improvements of line edge roughness and restraint of resist profile fluctuation due to PED (Post Exposure Delay) between exposure and PEB are required.
When a chemical amplification resist is applied to immersion exposure, it is appointed that since the resist layer inevitably touches an immersion liquid at the time of exposure, the resist layer decomposes and ingredients that adversely influence the immersion liquid ooze out from the resist layer. WO 2004/068242 discloses an example that the resist performance fluctuates by the immersion of a resist for ArF exposure in water before and after exposure, and appoints this is a problem in immersion exposure.
Further, when exposure is performed with a scanning system immersion exposure apparatus in an immersion exposure process, the speed of exposure lowers if an immersion liquid does not move following in the movement of a lens, so that there is the fear of influence on productivity. In the case where the immersion liquid is water, the resist film is preferably hydrophobic in view of good following ability of water. On the other hand, there arises adverse influence on the image performance of resist when the resist film is hydrophobic, such that generating amount of scum increases, and the improvement is required.